AX-ConfigurationUtility User Manual
15
4.2.
RX Synchronized with TX Mode
The purpose of
RX Synchronized with TX
mode is periodic reception of packets with
minimal current consumption by enabling the RX only for the time slots in which packets
are expected. Short preambles can be used on the TX side
2
. The following points explain
how the
RX Synchronized with TX
mode works:
•
RX Synchronized with TX
mode is used together with
TX periodic (LPXOSC)
on the TX side. Timing is driven by the MCU’s low power 32kHz tuning fork
crystal
oscillator which ensures an accurate packet frequency and thus allows for tight
margins in the time slots in which the RX is enabled.
•
After power up LPXOSC is settled and the RX is switched continuously on until a
packet is received, or a timeout occurs. LED1 indicates the RX is running. When a
packet is received the RX is put to sleep and only wakes up again for the time slot
in which the next packet is expected.
•
With each further packet reception, the RX measures the effective time elapsed
since the last packet and (via low pass filtering) corrects its own wake-up frequency
accordingly. This corrects for crystal variations as well as temperature differences
and slow gradients and minimizes required margins in the RX-on time slots. (An
increased margin is used for the packet reception right after synchronization, where
the effective period has not been measured yet.)
•
If no packet is received during an RX-on time slot, the RX margins are increased
for the next time slot. If no packet is received during N subsequent time slots, the
RX module switches back to synchronization mode, i.e. the RX is switched on
continuously until a packet is received or a timeout occurs. (This synchronization
mode is the same as for initial synchronization after power up. The only difference
lies in the timeout interval: A timeout (in seconds) can be configured for initial
synchronization after power-up (e.g. time to put batteries into the TX module). A
second timeout (in packet periods) applies for re-synchronization after losing
multiple packets in a row.
•
If (re-)synchronization fails, (no packet is received until the timeout), the RX
module is put to sleep for a configurable, typically long, period before trying to
synchronize again. The rationale here is to limit RX power consumption in the case
where the TX is off or out of reach.
•
The
Sync Timing
button opens the Sync Timing panel, where various timing
parameters can be configured.
2
This contrasts with the asynchronous nature of
Wake on Radio
mode, where a preamble is at least as long as
the RX sleep interval is required.
